Hunger games of the mind

I think, therefore I eat. Our thoughts and memory of eating may affect our appetite more than we realise, new research shows.

A study by the University of Bristol, published last week in the Plos One Journal, found that how much we think we have eaten, as opposed to much how much we have actually eaten, affects our sense of being satiated. So, hunger, several hours after a meal, can be predicted by our perception of how much food we remember seeing in front of us.

To test the theory, 100 adult participants were shown either a small (300 millilitre) or large (500 millilitre) bowl of creamed tomato soup before lunch. They were then given a bowl of soup and told to consume the entire serving.

Using hidden tubes at the bowl's base, scientists adjusted the amount of soup eaten by participants and found that immediately after the meal, those who had, consciously or not, consumed a 500 ml bowl of soup, reported being more satiated.

"We attribute this to the immediate proximal effect of the food promoting neural and endocrine signalling," the authors said - a finding that is consistent with the traditional school of thought that appetite is dictated by our endocrine system's signals, which return our bodies to balance when we are sufficiently satiated.

But, two to three hours after the meal, hunger no longer matched the actual amount consumed. Instead, even after after balancing for age, gender, and initial hunger, the researchers found that participants who saw the 500 ml bowl of soup reported greater satiety than those shown the 300 ml bowl, regardless of which size bowl they ended up eating.

"Participants who thought they had consumed the larger 500-ml portion reported significantly less hunger. This was also associated with an increase in the 'expected satiation' of the soup 24-hours later," the authors said.

It is not the first time research has shown perception plays an important part in appetite. We know, of course, that most people don't eat purely for survival, but for palatability and pleasure too. This can have an important influence on the amount eaten. What we eat and the amount we eat can also be affected by those around us.

In addition to this, it has previously been found that amnesia sufferers may eat more meals than they need because they have forgotten the previous one. Despite this, they still report little change in their hunger. But, it has been said that this may be due to damage in the to hunger-regulating receptors of these subjects' brains.

In light of this, the study authors said that, "for the first time, this manipulation exposes the independent and important contribution of memory processes to satiety. Opportunities exist to capitalise on this finding to reduce energy intake in humans."